In Finland 25 % of the total energy consumption is used for heating buildings. Majority of apartment blocks in Finland are built in 1960 – 1970 century and energy efficiency in those buildings is rather weak. Apartment blocks built in that era use mainly mechanical exhaust air ventilation system and 35 – 40 % of the buildings heat loss is due to the ventilation system, when warm air from the inside is blown away through the ventilation system. With exhaust air heat recovery systems this warm air is possible to collect and use it with a heat pump in the building’s heating system and warm water system.
The objective of this thesis was to create a calculation model to determine cost-effectiveness of heat recovery system from exhaust air in apartment blocks that takes into account a relevant amount of data and is accurate enough but also easy to use. Calculation model is based on two different method, simulation of the building’s energy consumption is based on the National Building Code of Finland D5 with some adaptions and calculation of the energy produced by heat pump is based on research of VTT Technology “Renewable energy production of Finnish heat pumps”. Calculation is made for every hour during one year.
Profitability of the exhaust air heat recovery system investment is estimated by the savings in energy costs in a year when the need of district heating has decreased. Investment is evaluated by payback period and net present value during the observation period. Sensitivity analysis is made for changes in electricity and district heating prices.
Calculation model was used to model the energy consumption in an example building built in 1960 and then calculating the amount of energy produced by the heat pump from the heat recovery of exhaust air. As a result of the calculation the energy consumption in the example building can be reduced 46 % by using the exhaust air heat recovery system. Heat recovery system and heat pump increase the electricity consumption by 62 %. Payback period for the investment with the used variables is 12 years. The results are dependent on the used input data and have a significant effect on the accuracy of the calculation.